Nickel brazed articles

ABSTRACT

Brazing of metal parts employing a thin, homogeneous, ductile, filler metal foil is disclosed. The brazing foil, useful for brazing stainless steels, is less than about 0.0025 inch thick and has a composition consisting essentially of 0 to about 4 atom percent iron, 0 to about 21 atom percent chromium, 0 to about 19 atom percent boron, 0 to about 12 atom percent silicon, 0 to about 22 atom percent phosphorus and the balance nickel and incidental impurities. In addition to containing the foregoing elements within the above-noted composition ranges, the composition must be such that the total of iron, chromium and nickel ranges from about 76 to 84 atom percent and the total of boron, silicon and phosphorus ranges from about 16 to 24 atom percent. The ductile foil permits fabrication of preforms of complex shapes which do not require binders and/or fluxes necessary for brazing powders presently used to braze stainless steels and nickel base alloys.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser.No. 008,370, filed Feb. 1, 1979, now abandoned, entitled "HomogeneousDuctile Brazing Foils" which, in turn, is a continuation-in-part ofcopending application Ser. No. 912,667, filed June 5, 1978, now U.S.Pat. No. 4,148,973 which, in turn, is a continuation of application Ser.No. 751,000, filed Dec. 15, 1976, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to brazing of metal parts and, in particular, toa homogeneous, ductile brazing material useful in brazing stainlesssteels and high nickel alloys.

2. Description of the Prior Art

Brazing is a process for joining metal parts, often of dissimilarcomposition, to each other. Typically, a filler metal that has a meltingpoint lower than that of the metal parts to be joined together isinterposed between the metal parts to form an assemby. The assembly isthen heated to a temperature sufficient to melt the filler metal. Uponcooling, a strong, corrosion resistant, leak-tight joint is formed.

As a class, stainless steel alloys are more difficult to braze than arecarbon and low-alloy steels. This is apparently due to the high chromiumcontent associated with stainless steels. The formation of chromiumoxide on the surfaces of stainless steels prevents wetting by the moltenmetal filler. Consequently, heating and brazing must be performed oncarefully cleaned metal parts either in vacuum or under stronglyreducing conditions, such as dry hydrogen or cracked ammonia.Alternatively, chemically active fluxes which dissolve the oxide must beused. However, extensive post-brazing cleaning is required to removeflux residues.

The brazing alloys suitable for use with stainless steels, designatedAWS BNi compositions, contain a substantial amount (about 3 to 11 weightpercent) of metalloid elements such as boron, silicon and/or phosphorus.Consequently, such alloys are very brittle and are available only aspowder, powder-binder pastes, powder-binder tapes and bulky castpreforms. Powders are generally unsuitable for many brazing operations,such as dip brazing, and do not easily permit brazing of complex shapes.Although some powders are available as pastes employing organic binders,the binders form objectionable voids and residues during brazing.

Some brazing alloys are available in foil form. Such materials are (1)fabricated through a costly sequence of rolling and carefulheat-treating steps, (2) prepared by powder metallurgical techniques or(3) fabricated by quenching a melt of the alloy on a rotating quenchwheel at a rate of at least about 10⁵ ° C./sec. Rolled foil is notsufficiently ductile to permit stamping of complex shapes therefrom.Powder metallurgical foil is not homogeneous and employs binders, whichform objectionable voids and residues during brazing. Quenched foil,disclosed by U.S. Pat. No. 4,148,973, represents a substantialimprovement over powdered and rolled foils, but has a thickness (about0.0015 to 0.0025 inch) somewhat greater than that which has now beenfound to be required for maximum joint strength.

Ductile glassy metal alloys have been disclosed in U.S. Pat. No.3,856,513, issued Dec. 24, 1974 to H. S. Chen et al. These alloysinclude compositions having the formula M_(a) Y_(b) Z_(c), where M is ametal selected from the group consisting of iron, nickel, cobalt,vanadium and chromium, Y is an element selected from the groupconsisting of phosphorus, boron and carbon, and Z is an element selectedfrom the group consisting of aluminum, silicon, tin, germanium, indium,antimony and beryllium, "a" ranges from about 60 to 90 atom percent, "b"ranges from about 10 to 30 atom percent and "c" ranges from about 0.1 to15 atom percent. Also disclosed are glassy wires having the formulaT_(i) X_(j), where T is at least one transition metal and X is anelement selected from the group consisting of phosphorus, boron, carbon,aluminum, silicon, tin, germanium, indium, beryllium and antimony, "i"ranges from about 70 to 87 atom percent and "j" ranges from about 13 to30 atom percent. Such materials are conveniently prepared by rapidquenching from the melt using processing techniques that are nowwell-known in the art. No brazing compositions are disclosed therein,however.

There remains a need in the art for a homogeneous, brazing material thatis available in thin, ductile foil form.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a homogeneous,ductile brazing foil useful as a filler metal for a brazed metalarticle. The brazing foil is composed of metastable material having atleast 50 percent glassy structure, and has a thickness less than about0.0025 inch. It has been found that use of a brazing foil that isflexible, thin and homogeneous, as described above, improves braze jointstrength, enhances joining precision and reduces process time.

More specifically, the brazing foil has a thickness of about 0.0005 to0.0014 inch. Preferably, such foil has a composition consistingessentially of 0 to about 4 atom percent iron, 0 to about 21 atompercent chromium, 0 to about 19 atom percent boron, 0 to about 12 atompercent silicon, 0 to about 22 atom percent phosphorus and the balanceessentially nickel and incidental impurities. In addition to containingthe foregoing elements within the above-noted composition ranges, thecomposition must be such that the total of iron, chromium and nickelranges from about 76 to 84 atom percent and the total of boron, siliconand phosphorus constitutes the remainder, that is, about 16 to 24 atompercent.

The homogeneous brazing foil of the invention is fabricated by a processwhich comprises forming a melt of the composition and quenching the melton a rotating quench wheel at a rate of at least about 10⁵ ° C./sec.

The filler metal foil is easily fabricable as homogeneous, ductileribbon, which is useful for brazing as cast. Advantageously, the metalfoil can be stamped into complex shapes to provide braze preforms.

Further, the homogeneous, ductile brazing foil of the inventioneliminates the need for binders and pastes that would otherwise formvoids and contaminating residues. Also, the filler material provided bythe invention enables alternative brazing processes of stainless steels,e.g., dip brazing in molten salts, to be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages willbecome apparent when reference is made to the following detaileddescription of the preferred embodiments of the invention and theaccompanying drawing, which is a graph showing the relationship betweenthickness and shear strength of a brazed joint incorporating theelements of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In any brazing process, the brazing material must have a melting pointthat will be sufficiently high to provide strength to meet servicerequirements of the metal parts brazed together. However, the meltingpoint must not be so high as to make difficult the brazing operation.Further, the filler material must be compatible, both chemically andmetallurgically, with the materials being brazed. The brazing materialmust be more noble than the metal being brazed to avoid corrosion.Ideally, the brazing material must be in ductible foil form so thatcomplex shapes may be stamped therefrom. Finally, the brazing foilshould be homogeneous, that is, contain no binders or other materialsthat would otherwise form voids or contaminating residues duringbrazing.

In accordance with the invention, a homogeneous, ductile brazingmaterial in foil form is provided. The brazing foil is less than 0.0025inch thick, preferably about 0.0015 to 0.0025 inch thick and mostpreferably about 0.0005 to 0.0014 inch thick. Preferably, the brazingfoil has a composition consisting essentially of 0 to about 4 atompercent iron, 0 to about 21 atom percent chromium, 0 to about 19 atompercent boron, 0 to about 12 atom percent silicon, 0 to about 22 atompercent phosphorus and the balance essentially nickel and incidentalimpurities. The composition is such that the total of iron, chromium andnickel ranges from about 76 to 84 atom percent and the total of boron,silicon and phosphorus comprises the balance, that is, about 16 to 24atom percent. These compositions are compatible with and more noble thanstainless steels and are suitable for brazing austenitic, martensiticand ferritic stainless steels, as well as nickel base alloys.

By homogeneous is meant that the foil, as produced, is of substantiallyuniform composition in all dimensions. By ductile is meant that the foilcan be bent to a round radius as small as ten times the foil thicknesswithout fracture.

Examples of brazing alloy compositions within the scope of the inventionare set forth in Table I below.

                  TABLE I                                                         ______________________________________                                                      Composition, %                                                                Fe  Ni     Cr     B    Si   P                                   ______________________________________                                        Ni--P atom %    --    81     --   --   --   19                                weight %        --    89     --   --   --   11                                Ni--Cr--P atom %                                                                              --    68.6   14.3 --   --   17.1                              weight %        --    76     14   --   --   10                                Ni--Si--B(1) atom %                                                                           --    80.9   --   9.0  10.1 --                                weight %        --    92.4   --   1.9  5.5  --                                Ni--Si--B(2) atom %                                                                           --    78     --   14   8    --                                weight %        --    92.4   --   3.1  4.5  --                                Ni--Cr--Fe--Si--B atom %                                                                      2.7   68.8   6.6  14.0 7.9  --                                weight %        3     82.4   7    3.1  4.5  --                                Ni--Cr--B atom %                                                                              --    69.4   14.4 16.2 --   --                                weight %        --    81.5   15   3.5  --   --                                Ni--Cr--Fe--Si--B atom %                                                                      3.5   63.5   12.3 12.8 7.9  --                                weight %        4     75.7   13   2.8  4.5  --                                Ni--Cr--Fe--Si--B atom %                                                                      3     66     7    18   6    --                                weight %        3.5   81.2   7.7  4.1  3.5  --                                Ni--Cr--Fe--Si--B atom %                                                                      3     59     18   16   4    --                                weight %        3.4   71.4   19.3 3.6  2.3  --                                ______________________________________                                    

The brazing temperature of the brazing alloys of the invention rangesfrom about 925° to 1205° C. (1700° to 2200° F.). The temperature ofbrazing is thus above the sensitizing temperature range of the 300series stainless steels. This is in contrast to the brazing temperaturesof silver brazing alloys, which fall within the sensitizing temperaturerange. As is well-known, when 18-8 stainless steels are heated at about510° to 790° C. (950° to 1450° F.) for any appreciable length of time,they become sensitized or susceptible to intergranular corrosion. Thisis apparently due to the depletion of chromium in the grain-boundaryareas. Sensitizing is thus avoided by use of the brazing foils of theinvention.

The brazing foils of the invention are prepared by cooling a melt of thedesired composition at a rate of at least about 10⁵ ° C./sec, employingmetal alloy quenching techniques well-known to the glassy metal alloyart; see, e.g., U.S. Pat. Nos. 3,856,513 and 4,148,973, discussedearlier. The purity of all compositions is that found in normalcommercial practice.

A variety of techniques are available for fabricating continuous ribbon,wire, sheet, etc. Typically, a particular composition is selected,powders or granules of the requisite elements in the desired portionsare melted and homogenized, and the molten alloy is rapidly quenched ona chill surface, such as a rapidly rotating metal cylinder.

Under these quenching conditions, a metastable, homogeneous, ductilematerial is obtained. The metastable material may be glassy, in whichcase there is no long range order. X-ray diffraction patterns of glassymetal alloys show only a diffuse halo, similar to that observed forinorganic oxide glasses. Such glassy alloys must be at least 50% glassyto be sufficiently ductile to permit subsequent handling, such asstamping complex shapes from ribbons of the alloys. Preferably, theglassy metal alloys must be at least 80% glassy, and most preferablysubstantially (or totally) glassy, to attain superior ductility.

The metastable phase may also be a solid solution of the constituentelements. In the case of the alloys of the invention, such metastable,solid solution phases are not ordinarily produced under conventionalprocessing techniques employed in the art of fabricating crystallinealloys. X-ray diffraction patterns of the solid solution alloys show thesharp diffraction peaks characteristic of crystalline alloys, with somebroadening of the peaks due to desired fine-grained size ofcrystallites. Such metastable materials are also ductile when producedunder the conditions described above.

The brazing material of the invention is advantageously produced in foil(or ribbon) form, and may be used in brazing applications as cast,whether the material is glassy or a solid solution. Alternatively, foilsof glassy metal alloys may be heat treated to obtain a crystallinephase, preferably fine-grained, in order to promote longer die life whenstamping of complex shapes is contemplated.

Foils as produced by the processing described above typically are about0.0005 to 0.0025 inch thick, which is also the desired spacing betweenbodies being brazed. Foil thickness, and hence spacing of about 0.0005to 0.0014 inch maximizes the strength of the braze joint. Thinner foilsstacked to form a thickness of greater than 0.0025 inch may also beemployed. Further, no fluxes are required during brazing, and no bindersare present in the foil. Thus, formation of voids and contaminatingresidues is eliminated. Consequently, the ductile brazing ribbons of theinvention provide both ease of brazing, by eliminating the need forspacers, and minimal post-brazing treatment.

In general, the strength of the resulting brazed joints is generally atleast equal to that of brazed joints prepared from conventional powderbrazes of the same composition. With alloys based on the Ni-B-Si system,braze joints made with thin ductile brazing ribbons of the invention areconsistently stronger than joints made with thicker ribbon or withpaste. With alloys based on the Ni-P system, braze joints made withribbon and paste exhibit approximately the same shear strength. Withoutsubscribing to any particular theory, it appears that the lower surfacearea of the ribbon, which would be less susceptible to oxidation thanpowder, and the greater area of contact between base metal and ribbon ascompared with base metal and powder contribute significantly to jointstrength.

The brazing foils of the invention are also superior to various powderbrazes of the same composition in providing good braze joints. This isprobably due to the ability to apply the brazing foil where the braze isrequired, rather than depending on capillarity to transport braze fillerfrom the edge of surfaces to be brazed.

EXAMPLES Example 1

Ribbons about 2.5 to 25.4 mm (about 0.10 to 1.00 inch) wide and about 13to 60 μm (about 0.0005 to 0.0025 inch) thick were formed by squirting amelt of the particular composition by overpressure of argon onto arapidly rotating copper chill wheel (surface speed about 3000 to 6000ft/min). Metastable, homogeneous ribbons of substantially glassy alloyshaving the following compositions in weight percent and atom percentwere produced:

    ______________________________________                                               Composition                                                            Sample No.                                                                             Fe      Ni      Cr    B     Si    P                                  ______________________________________                                        1   (wt %)   3.0     82.4  7     3.1   4.5   --                                   (at %)   2.7     68.8  6.6   14.0  7.9   --                               2   (wt %)   --      89    --    --    --    11                                   (at %)   --      81    --    --    --    19                               3   (wt %)   --      76    14    --    --    10                                   (at %)   --      68.6  14.3  --    --    17.1                             4   (wt %)   --      92.4  --    1.9   5.5   --                                   (at %)   --      80.9  --    9.0   10.1  --                               5   (wt %)   --      81.5  15    3.5   --    --                                   (at %)   --      69.4  14.4  16.2  --    --                               6   (wt %)   --      92.4  --    3.1   4.5   --                                   (at %)   --      78    --    14    8     --                               7   (wt %)   4       75.7  13    2.8   4.5   --                                   (at %)   3.5     63.5  12.3  12.8  7.9   --                               8   (wt %)   3.5     81.2  7.7   4.1   3.5   --                                   (at %)   3       66    7     18    6     --                               9   (wt %)   3.4     71.4  19.3  3.6   2.3   --                                   (at %)   3       59    18    16    4     --                               ______________________________________                                    

Example 2

Tensile test specimens were cut from AISI types 430SS and 304SS in stripform. The thicknesses were both 0.036 inch. A brazing alloy of theinvention, a glassy, ductile ribbon of nominal composition of Sample No.2 within specification AWS A5.8-76 for BNi6 and having dimensions 0.0017inch thick by 0.175 inch wide, was used to braze some of the testspecimens. For comparison, a brazing paste of the same composition andspecification, sold under the trade designation Nicrobraz® 10 (availablecommercially from Wall-Colmonoy Co. of Detroit, Michigan), was used tobraze other test specimens.

The tensile specimens were dimensioned and fabricated per ASTM D638 andwere of the type I variety. The tensile specimens were cutperpendicularly to the length direction at the mid-point of the length.Braze joints were of the lap type, with the lap dimension carefullycontrolled to 3/8 inch or 1/2 inch (for type 430 stainless steel) or 5/8inch or 3/4 inch (for type 304 stainless steel). Uncut tensile specimenswere kept as controls to determine tensile properties after the brazingcycle. Brazing specimens were degreased with warm benzene. Lap jointscontaining brazing ribbons of the invention were assembled with eitherone ribbon or four ribbons side-by-side the length of the lap joint. Inthe case of these brazing alloys, the ribbons acted as the spacers. Asingle spot weld was used to hold the assembly together, as is commonindustrial practice.

Identical lap joints were prepared for use with the brazing paste. Aspacer of 0.0015 inch type 410 stainless steel approximately 0.19 inchby 0.15 inch was used, as is conventional when employing brazing pastes.A single spot weld was made, employing identical welding parameters asabove. Braze specimens utilizing the brazing paste had the paste appliedin the prescribed manner as practiced commercially.

Brazing was done in a belt furnace with a dry, cracked ammoniaatmosphere. The furnace was operated at 1900° F. at 1 ft/min. The lengthof the hot zone was 8 ft.

Upon brazing, all shear specimens and stainless steel controls weresubjected to tensile shear testing, with the following results:

    ______________________________________                                                       Joint Shear Strength, psi                                      Metal    Braze Filler                                                                              Range         Avg.                                       ______________________________________                                        304SS    brazing paste                                                                             3,733-4,933    4,208                                     304SS    1 ribbon    2,747-5,627    4,165                                     304SS    4 ribbons   3,000-4,320    3,380                                     430SS    brazing paste                                                                             >4,267->6,160 >5,698                                     430SS    1 ribbon    >5,493->5,893 >5,693                                     430SS    4 ribbons   >6,880        >6,880                                     ______________________________________                                    

The ultimate tensile strength of controls after brazing cycle was asfollows:

AISI 304: 93,300 psi

AISI 430: 102,800 psi

The brazes on 430SS were observed to be stronger in general than on304SS. As is well-known, thin brazes are subjected to triaxial stressconditions, and the resultant stress at failure is a function of theultimate tensile stress of both the braze filler metal and the basemetal. Since 430 stainless steel has a higher ultimate tensile strengththan 304 stainless steel, brazed joints of 430 stainless steel appear tobe stronger than brazed joints of 304 stainless steel.

All 430SS brazes were observed to fail in the base metal and not in thebraze; therefore, the values reported are lower bounds.

Example 3

Tensile test specimens of AISI 430SS and 304SS were prepared for brazingas in Example 2. A brazing alloy of the invention, a glassy ductileribbon of nominal composition of Sample No. 3 within specification AWSA5.8-76 for BNi7 and having dimensions 0.0021 inch thick by 0.106 inchwide was used to braze six test specimens. Two ribbons side-by-sideplaced the length of the lap joint were used. For comparison, a brazingpaste of the same composition and specification, sold under the tradedesignation Nicrobraz® 50 was used to braze six test specimens.

Brazing was done in a belt furnace with a dry, cracked ammoniaatmosphere. The furnace was operated at 1950° F. at 0.4 ft/min. Thelength of the hot zone was 8 ft.

The brazed joints evidenced the following joint shear strengths:

    ______________________________________                                                          Joint Shear Strength, psi                                   Metal      Braze Filler Range       Avg.                                      ______________________________________                                        304SS      brazing paste                                                                              3,620-4,600 4,050                                     304SS      2 ribbons    3,320-4,220 3,790                                     ______________________________________                                    

In all the 430SS specimens, the base metal failed before the braze.

Of the six specimens brazed with brazing foil of the invention, goodbrazes were obtained in all cases. Of the six specimens brazed withbrazing paste, good brazes were obtained in all cases.

Example 4

Tensile test specimens of AISI 430SS and 304SS were prepared for brazingas in Example 2. A brazing alloy of the invention, a glassy ductileribbon of nominal composition of Sample No. 6 within specification AWSA5.8-76 for BNi3 and having dimensions 0.0021 inch thick by 0.108 inchwide was used to braze six test specimens. Two ribbons side-by-sideplaced the length of the lap joint were used. For comparison, a brazingpaste of the same composition and specification, sold under the tradedesignation Nicrobraz® 130, was used to braze six test specimens.

Brazing was done in a vacuum furnace which was evacuated to 0.1 μm thenback-filled with N₂ to a partial pressure of 100 μm. The furnace washeld at 1900° F. for 15 minutes.

The brazed joints evidenced the following joint shear strengths:

    ______________________________________                                                         Joint Shear Strength, psi                                    Metal      Braze Filler                                                                              Range        Avg.                                      ______________________________________                                        304SS      brazing paste                                                                             5,950-11,360 7,645                                     304SS      2 ribbons   7,900-10,510 9,050                                     ______________________________________                                    

In all the 430SS specimens, the base metal failed before the braze.

Of the six specimens brazed with brazing foil of the invention, goodbrazes were obtained in all cases. Of the six specimens brazed withbrazing paste, good brazes were obtained in only four cases.

Example 5

Tensile test specimens of AISI 430SS and 304SS were prepared for brazingas in Example 2. A brazing alloy of the invention, a glassy ductileribbon of the nominal composition of Sample No. 1 within specificationAWS A5.8-76 for BNi2 and having dimensions 0.0016 inch thick by 0.205inch wide was used to braze six test specimens. One ribbon placed thelength of the lap joint was used. For comparison, a brazing paste of thesame composition and specification, sold under the trade designationNicrobraz® LM, was used to braze six test specimens.

Brazing was done in a vacuum furnace as in Example 4.

The brazed joints evidenced the following joint shear strengths:

    ______________________________________                                                         Joint Shear Strength, psi                                    Metal      Braze Filler                                                                              Range        Avg.                                      ______________________________________                                        304SS      brazing paste                                                                             5,310-8,630  6,940                                     304SS      1 ribbon    8,910-11,380 9,680                                     ______________________________________                                    

In all the 430SS specimens, the base metal failed before the braze.

Of the six specimens brazed with brazing foil of the invention, goodbrazes were obtained in all cases. Of the six specimens brazed withbrazing paste, good brazes were obtained in only three cases.

Example 6

Test specimens were cut from 0.125 inch thick AISI type 316SS strip.Brazing alloy of the invention of nominal composition of Sample No. 8,6.5 mm (0.25 inch) wide and 50 μm (0.002 inch) thick was used to brazethree test specimens. Brazing alloy of the invention of nominalcomposition of Sample No. 9, 6.5 mm (0.25 inch) wide and 40 μm (0.0015inch) thick was used to braze three test specimens.

Lap shear test specimens were prepared as per AWS C3.2. The lapdimension was carefully controlled at 0.375 inch (3× thickness of thebase metal).

Brazing was done in a vacuum furnace. The furnace was evacuated to 0.1μm and operated at 1900° F. for 15 minutes.

Upon brazing, all shear specimens were subjected to tensile sheartesting, with the following results:

    ______________________________________                                                          Joint Shear Strength, psi                                   Metal  Braze Filler     Range       Avg.                                      ______________________________________                                        316SS  3 ribbons, Sample No. 8                                                                        18,260-18,347                                                                             18,289                                    316SS  3 ribbons, Sample No. 9                                                                        14,667-18,560                                                                             16,242                                    ______________________________________                                    

In all cases, test specimens brazed with Sample No. 8 failed in the basemetal. Therefore, the values reported are lower bounds. Two of the threetest specimens brazed with Sample No. 9 failed in the joint. The thirdtest specimen failed in the base metal.

Of the six specimens brazed in this example, good brazes were obtainedin all cases.

Example 7

Test specimens were cut from 0.125 inch thick AISI 316SS strip. Brazingalloy of the invention of nominal composition of Sample No. 8, 12.7 mm(0.5 inch) wide and 25 μm (0.001 inch) thick, was used to braze twosamples. Five layers of ribbon were stacked in the joint area. A jointspacer was used to set the final joint thickness at 127 μm (0.005 inch).

Lap shear test specimens were prepared as per AWS C3.2. The lapdimension was carefully controlled at 0.25 inch (2× thickness of thebase metal).

Brazing was done in a vacuum furnace. The furnace was evacuated to 0.1μm and operated at 1900° F. for 10 minutes.

Upon brazing, all shear specimens were subject to tensile shear testingwith the following results:

    ______________________________________                                                          Joint Shear Strength, psi                                   Metal  Braze Filler     Range       Avg.                                      ______________________________________                                        316SS  5 ribbons, Sample No. 8                                                                        13,520-13,760                                                                             13,640                                    ______________________________________                                    

Example 8

Test specimens were cut from 0.125 inch thick AISI 316SS strip. Brazingalloy of the invention of nominal composition of Sample No. 8, 12.7 mm(0.5 inch) wide and 25 μm (0.001 inch) thick, was used to braze threesamples. Three layers of ribbon were stacked in the joint area. A jointspacer was used to set the final joint thickness at 76 μm (0.003 inch).

Lap shear test specimens were prepared as per AWS C3.2. The lapdimension was carefully controlled at 0.25 inch (2× thickness of thebase metal).

Brazing was done in a vacuum furnace. The furnace was evacuated to 0.1μm and operated at 1900° F. for 10 minutes.

Upon brazing, all shear specimens were subject to tensile shear testingwith the following results:

    ______________________________________                                                          Joint Shear Strength, psi                                   Metal  Braze Filler     Range       Avg.                                      ______________________________________                                        316SS  3 ribbons, Sample No. 8                                                                        12,700-15,520                                                                             14,743                                    ______________________________________                                    

Example 9

Test specimens were cut from 0.125 inch thick AISI 316SS strip. Brazingalloy of the invention of nominal composition of Sample No. 8, 12.7 mm(0.5 inch) wide and 25 μm (0.001 inch) thick, was used to braze onesample. One layer of ribbon was placed in the joint area. A joint spacerwas used to set the final joint thickness at 25 μm (0.001 inch).

Lap shear test specimens were prepared as per AWS C3.2. The lapdimension was carefully controlled at 0.25 inch (2× thickness of thebase metal).

Brazing was done in a vacuum furnace. The furnace was evacuated to 0.1μm and operated at 1900° F. for 10 minutes.

Upon brazing, all shear specimens were subject to tensile shear testingwith the following results:

    ______________________________________                                                          Joint Shear Strength, psi                                   Metal  Braze Filler     Range      Avg.                                       ______________________________________                                        316SS  1 ribbon, Sample No. 8                                                                         22,500     --                                         ______________________________________                                    

Example 10

Test specimens were cut from 0.125 inch thick AISI 316SS strip. Brazingalloy of the invention of nominal composition of Sample No. 8, 12.7 mm(0.5 inch) wide and 25 μm (0.001 inch) thick, was used to braze threesamples. One layer of ribbon was placed in the joint area. A jointspacer was used to set the final joint thickness at 13 μm (0.0005 inch).The excess filler metal formed a fillet around the joint.

Lap shear test specimens were prepared as per AWS C3.2. The lapdimension was carefully controlled at 0.25 inch (2× thickness of thebase metal).

Brazing was done in a vacuum furnace. The furnace was evacuated to 0.1μm and operated at 1900° F. for 10 minutes.

Upon brazing, all shear specimens were subject to tensile shear testingwith the following results:

    ______________________________________                                                          Joint Shear Strength, psi                                   Metal  Braze Filler     Range       Avg.                                      ______________________________________                                        316SS  1 ribbon, Sample No. 8                                                                         31,680-36,320                                                                             33,653                                    ______________________________________                                    

Example 11

Test specimens were cut from 0.125 inch thick AISI 316SS strip. Brazingalloy of the invention of nominal composition of Sample No. 8, 0.64 mm(0.25 inch) wide and 15 μm (0.0006 inch) thick, was used to braze foursamples. One layer of ribbon was placed in the joint area. A jointspacer was not used. The final joint thickness was 15 μm (0.0006 inch).

Lap shear test specimens were prepared as per AWS C3.2. The lapdimension was carefully controlled at 0.25 inch (2× thickness of thebase metal).

Brazing was done in a vacuum furnace. The furnace was evacuated to 0.1μm and operated at 1900° F. for 10 minutes.

Upon brazing, all shear specimens were subject to tensile shear testingwith the following results:

    ______________________________________                                                          Joint Shear Strength, psi                                   Metal  Braze Filler     Range       Avg.                                      ______________________________________                                        316SS  1 ribbon, Sample No. 8                                                                         6,640-28,400                                                                              14,740                                    ______________________________________                                    

The data of Examples 7 to 10 demonstrate increased joint strength withdecreasing thickness, provided that a sufficient amount of filler metaloccupies the joint volume. This is illustrated in FIG. 1. However, atsmall joint clearances, it becomes more difficult for the molten fillermetal to adequately distribute itself throughout the entire joint. If aninsufficient amount of filler metal is used, or if extensive flow of thefiller metal is required, as in Example 11 where a thin filler metalfoil was employed, joint strength will be reduced.

What is claimed is:
 1. A brazed metal article, said article having beenbrazed with a filler metal in the form of a homogenous, ductile brazingfoil composed of metastable material having at least 50% glassystructure and a composition consisting essentially of 0 to about 4 atompercent iron, 0 to about 21 atom percent chromium, 0 to about 19 atompercent boron, 0 to about 12 atom percent silicon, 0 to about 22 atompercent phosphorus and the balance essentially nickel and incidentalimpurities, wherein the composition is such that the total of iron,chromium and nickel ranges from about 76 to 84 atom percent and thetotal of boron, phosphorus and silicon ranges from about 16 to 24 atompercent.
 2. The brazed metal article of claim 1 which is at least about80% glassy.
 3. The brazed metal article of claim 1 which issubstantially glassy.
 4. The brazed metal article of claim 1 having athickness ranging from about 0.0015 to 0.0025 inch.
 5. A brazed metalarticle, said article having been brazed with a filler metal in the formof a homogeneous, ductile brazing foil composed of metastable materialhaving at least 50% glassy structure and a composition consistingessentially of 0 to about 4 atom percent iron, 0 to about 21 atompercent chromium, 0 to about 19 atom percent boron, 0 to about 12 atompercent silicon, 0 to about 22 atom percent phosphorus and the balanceessentially nickel and incidental impurities, wherein the composition issuch that the total of iron, chromium and nickel ranges from about 76 to84 atom percent and the total of boron, phosphorus and silicon rangesfrom about 16 to 24 atom percent, said foil having a thickness less thanabout 0.0025 inch.
 6. The brazing foil of claim 5 which is at leastabout 50% glassy.
 7. The brazed metal article of claim 5 which is atleast about 80% glassy.
 8. The brazed metal article of claim 5 which issubstantially glassy.
 9. The brazed metal article of claim 5 having athickness ranging from about 0.0005 to 0.0014 inch.